1. Field of the Invention
The present disclosure relates to collimator apparatuses, radiation systems, and methods for controlling collimators.
2. Description of the Related Art
The present disclosure relates to radiation collimator apparatuses and radiation therapy systems using the collimator apparatuses.
In radiation (e.g., X-ray) therapy, X-ray is need to be emitted to affected part that is to be irradiated in a manner such that abnormal cells such as cancer cells are precisely irradiated while normal cells are irradiated as little as possible. However, various shapes of cancer may be found in human body (the object to be irradiated), and the living human body may slightly moves even when a patient silently rests such as in a lying state. The slight movement of human body is caused by movement (e.g., breathing, heartbeat) of lungs, heart, and the like.
In order to follow such movement of organs, a method for achieving “moving body tracking” is proposed, in which a X-ray generation unit, X-ray collimator, etc., is moved so as to have the irradiation field follow the movement of affected part. In Japanese Unexamined Patent Application Publication No. H5-253309, a radiation therapy apparatus for moving a line shaped detection unit that detects X-ray transmitted through the affected part of patient, and moves a movable collimator for limiting irradiation field, thereby keeping the transmitted X-ray within a width-range of the line-shaped detection unit is disclosed. Also, in Japanese Unexamined Patent Application Publication No. H5-337207, a stereotactic radiosurgery apparatus including first stereotactic radiosurgery collimator leaf and second stereotactic radiosurgery collimator leaf having inclined slit is disclosed, where the first stereotactic radiosurgery collimator leaf and second stereotactic radiosurgery collimators leaf are mounted on a irradiation view field forming collimator, and a position control of collimator hole formed at intersection of the slit holes is performed by moving the first stereotactic radiosurgery collimator and second stereotactic radiosurgery collimator. The above described apparatuses form required irradiation fields by appropriately controlling a pair of left collimator and right collimator.
In Japanese Unexamined Patent Application Publication No. 2004-65808, a radiation therapy apparatus, in which a generation source of electron beam and a deflected electromagnet are coupled by a vacuum rotary joint, including a gantry arm for holding a emission head having target or collimator is disclosed, where means for mechanically swinging and rotating the emission head about an axis which is parallel with a rotary axis of a gantry arm, and the axis passes a virtual ray source position. Further, the apparatus includes a means for moving the variable stops in an emission direction of electron beams in an arc-like shape, where the center of the ark corresponds to a position of the source of electron beam. According to the disclosed apparatus, swing operation of the emission head about the axis parallel to the rotation axis of the gantry arm is performed while the collimator is moved in a direction along the rotation axis of the gantry arm. Therefore, the variable stops are controlled to move in two directions. Consequently, the X-ray radiation can be appropriately performed even if the body of the patient moves.
In Japanese Unexamined Patent Application Publication No. 2007-267971 and Japanese Unexamined Patent Application Publication No. 2003-175117, a radiation apparatus is disclosed, in which a therapeutic X-ray generating source is fixed on a supporting base through a rotating mechanism equipped with two mutually-perpendicular rotation axes (gimbal mechanism). The rotating mechanism is controlled so as to direct the irradiation axis to the isocenter. Independently from the rotating mechanism, the position of the source is adjusted in the directions of two axes through a positioning mechanism with respect to the supporting base. According to the disclosed apparatus, directions of the irradiation axis and the central axis of the collimator fixed at the supporting base are adjusted so as to be directed to the isocenter by the rotating mechanism and the positioning mechanism. Therefore, the radiation of the affected part can be performed by setting the irradiation field in accordance with a shape of the affected part.
However, the apparatuses disclosed in Japanese Unexamined Patent Application Publications No. H5-253309 and No. H5-337207, which control the movement of a pair of right collimator and left collimator in only one direction, are not designed taking account of movement speed of the collimator and precision of formed irradiation field. Also, in the apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2004-65808, the gantry arm having the generation source of electron beam and the emission head having the target or collimator are coupled by the vacuum rotary joint. Therefore, instability of X-ray radiation system due to backlash of mechanical system cannot be avoided. Also, in order to form a desired irradiation field, very high precision of the mechanical system is required because a center position of swing operation of the emission head is separated from a center position of movement of the collimator. Further, it is difficult to achieve a high speed operation since the weight of the emission head including the deflected electromagnet, target, collimator, etc., is large. As described above, although a two-dimensional swing operation can be performed, the “moving body tracking” is unlikely achieved by using technologies of related arts.
Apparatuses, disclosed in Japanese Unexamined Patent Application Publications No. 2007-267971 and No. 2003-175117, have a configuration in which the entire therapy radiation source is designed by using the gimbal mechanism so as to enable a control of directivity angle by rotating the X-ray radiation axis about two axes. Therefore, a scale and a weight of the apparatus become great. Therefore, it is difficult to achieve a high speed operation of the control of directivity angle and a high speed operation of moving body tracking.